1. Field of the Invention
This invention relates to respiratory therapy devices and, more particularly, to the design and construction of an improved exhalation valve assembly that can be used in various volume ventilator circuits.
2. Description of the Prior Art
An example of a prior art exhalation valve assembly is disclosed in U.S. Pat. No. 4,241,756. As noted in that patent, volume ventilator circuits utilize an exhalation valve assembly to hold and maintain pressure within the circuit and selectively allow gases to be exhaled by the patient and to escape therefrom. Exhalation valve assemblies are comprised of a valve body having a gas inlet conduit, which forms a gas discharge port within the valve body, and a gas outlet conduit. A flexible diaphragm selectively closes off the discharge port during inhalation. When the patient exhales, the diaphragm is pushed away from the port so as to allow the exhaled gases to escape from the valve body through the gas outlet conduit.
Volume ventilators, in general, have different pressure holding capabilities depending on their particular application. One determinant of pressure holding capability is the ratio of the area of the diaphragm that extends across the chamber of the valve body (hereinafter referred to as "effective area") to the area of the gas discharge port. This ratio will hereinafter be referred to as the "valve area ratio."
One of the most widely used volume ventilators in the respiratory therapy field has a limited capability for holding elevated Positive End Expiration Pressure ("P.E.E.P.") when using a circuit with a valve assembly having a valve area ratio usually below 1.5. The valve assembly used in such a circuit is specifically designed to achieve a particular ratio and cannot be modified so as to be used in another circuit requiring a different ratio. Another popular volume ventilator is not dependent upon the valve area ratio for high P.E.E.P. pressures, but rather is dependent on the valve area ratio for low patient exhalation effort beyond P.E.E.P. pressures. The valve assembly is specifically designed to achieve the required valve area ratio and cannot be modified to provide a different ratio for use in a different machine. Thus, prior art volume ventilators have required the use of specifically designed valve assemblies in order to achieve the desired valve area ratio. Notwithstanding the increased costs of manufacturing one specific valve for one type of machine, the prior art has been unable to provide any interchangeability of such valve assemblies.
The prior art valve assembly disclosed in the previously mentioned patent provided a means of using the same exhalation valve assembly in volume ventilator circuits requiring different valve area ratios. This was accomplished by a removable ring member, which supported a portion of the diaphragm being used.
While this construction allowed great flexibility, it was often not fully utilized. That is, this prior art valve assembly was often not used without the ring member even though it could have been so used. In practice, the configuration most often used was to leave the ring member in place and use diaphragms of varying construction and material, thereby changing the pressure holding capability of the volume ventilator and the effective area of the diaphragm. This meant unnecessary complexity and unnecessarily greater manufacturing and parts costs. The present invention overcomes these problems by providing a valve assembly that provides for different pressure holding capabilities while eliminating the need for support members and for the removable ring member.